To the Editor The article by Richardson et al1 reporting the elevated levels of dichlorodiphenyldichloroethylene (DDE) in patients with Alzheimer disease raises the strong possibility that the missing link is the antitestosterone effect of many pesticides causing increased β-amyloid production.

Pesticides, including dichlorodiphenyltrichloroethane (DDT), and particularly their breakdown product DDE have been linked with both Alzheimer2 and Parkinson diseases.3 The exact mechanism of action has been intensely researched, with some favoring a direct action of the different toxins on the neurones and others an indirect action via their ability to induce oxidative stress, mitochondrial dysfunction, and α-synuclein fibrillization. However, there is general agreement that exposure to multiple pesticides, genetic factors, and traumatic brain injury can also predispose an individual to getting 1 or both of these conditions.